Stabilized alkaryl amine and process for preparing



Patented June 1947 STABILIZED ALKARYL AND PROCESS FOR PREPARING R b rt K- Sm th. Cranf Standard Oil Develo ration of Delaware No Drawing. Application December N- a signor to pment Company, a corpo- Serial No. 515,987

Claims.

This invention relates to the stabilization of aromatic amines against deterioration by discoloration, etc., during storage.

Aromatic amines such as aniline, toluidine, xylidine, etc, are normally substantiaally colorless when freshly prepared or freshly distilled, but tend to darken in color during storage, the undesirable results beingg-reat y accelerated by s or e e dv emperatures- The object of the present invention is to stabilize such aromatic amines against discoloration during storage.

Broadly, the invention comprises adding to the aromatic amines a small amount of a stabilizer comprising essentially an amine-soluble amphoteric metalor metalloid compound having a slight acid ionization reaction, such as boric acid and derivatives thereof.

Although the amount of the stabilizer to be used may vary according to the intended duration of storage and the temperature of storage, as well as according to the particular aromatic amine and the particular stabilizer used, in general about .01% to 1.0% of stabilizer will be sufiicient, and usually about .05% to 0.5% by weight of stabilizer will be found most practical for giving satisfactory results.

Although the invention is intended to apply broadly to the stabilization of any type of aromatic amines, it is believed particularly applicable to alkaryl amines, especially those having 1 to 3 alkyl carbon atoms. The invention has been found very successful for the stabilization of xylidine, either the pure separate isomers, or mixtures thereof. Other alkaryl amines which may be stabilized include the toluidines, ortho, meta or para, or mixtures thereof, the several ethyl anilines, cumidine (which is isopropylaniline), etc. Dialkylated and trialkylated aryl amines are preferred. Although the invention is particularly applicable to such alkaryl amines, it may also be used for stabilizing aniline, naphthylamines, and the various derivatives of aniline in which either or both of the hydrogens of the amino group are substituted by hydrocarbons, i.e., either alkyl or aryl groups, e.g., in N-monomethyl aniline, N-dimethyl aniline, N-monoethyl aniline, etc. Thus although the invention is particularly applicable to alkaryl primary amines, other amines such as secondary and tertiary amines may also be used.

The various above described aromatic amines may be used alone or together with a diluent, such as a hydrocarbon solvent, e. g., naphtha. Such diluents may be present in amounts ranging from 2 o ly a f w per cent. unto 1. 20 r'even 190 timese v lum o he r matic amin s when a ine ar a d d t oline for use as motor fuel.

n a r in t he invention, it is preferred to d h s a ilizer to he aromatic amines as soon as the latter has been prepared, or immediately after distillation.

The following experimental data will illustrate the advantages of the invention:

A sample of xylidine (a mixture of various isomeric xylidines) freshly redistilled in an atmosphere of C02, and which was a light straw color, was tested for color stability by heating in an open bottle for 10 hours at C. as an accelerated stability test. At the end of this time the optical density, which is an indication of discoloration or darkening of color, had increased from.02 to .33. On the other hand, 0.2% of boric acid, H3BO3, was added to another sample of the same redistilled xylidines and the mixture was simultaneously subjected to the same accelerated stability test. The mixture, which had an optical density of .02 at the beginning of the test, was found to still have an optical density of .07 at the end of the heating, thereby indicating that the 0.2% of boric acid had completely stabilized the xylidine against discoloration during the severe accelerated stability test. Observations at intermediate 2-hour periods are shown together with those results in the following tables:

Thus the discoloration without stabilizer was about 5 or 6 times as great as in the stabilized amine liquid.

In place of boric acid various derivatives thereof may be used such as alkyl boric acids, e, g., ethyl boric acid, C2H5B(OH)2, di-ethyl boric acid, (C2H5)BOH, butyl boric acid, C4H9B(OH)2, or other boric derivatives, e. g., tri-ethyl boron, (C2H5)3B, or other tri-alkyl boron compounds, or various alkyl, aryl, or other hydrocarbon borates, e. g., tri-ethyl borate, B(OC2H5)3. These various boron compounds may be classified broadly as having the general formula BRs, in which R represents hydrocarbon, hydrocarbon-oxy or hydroxy, and in which the hydrocarbon may be alkyl, aryl, aralkyl, alkaryl or cyclo-alkyl, etc. In place of the above boron compounds or mix- 3 tures thereof one may use amine-soluble compounds of other polyvalent amphoteric metals, such as aluminum, molybdenum, tungsten, and chromium, the preferred types of compounds being aluminates, molybdates, tungstates, and

chromates, respectively, such as, aluminum isopropoxide, aluminum butoxide, aluminum acetylacetonate, aluminum nitrate, molybdenum-blueoxide, molybdic-acid or chromic hydroxide.

Although the mechanism of the operation of the invention is not understood with certainty, it is believed that during the storage, the aromatic amine liquid may undergo some chemical reaction such as oxidation, polymerization or condensation which is subject to inhibition by the mildly acid-reacting stabilizer, which preferably should have a pH of about 4.5 to 5.5, or be equivalent to an acid having an ionization constant between about 10* and 10- It is not intended that this invention be limited to the particular materials which have been given merely for the sake of illustration, nor by any theory as to the mechanism of the operation of the invention, but only by the appended claims in which it is intended to claim all novelty inherent in the invention as well as all modifications coming within the scope and spirit of the invention.

I claim:

1. A composition comprising an alkaryl amine and a small but stabilizing amount of boric acid.

2. A composition comprising an alkaryl amine having from 1 to 3 alkyl carbon atoms, having added thereto a stabilizing amount of boric acid.

3. A mononuclear aromatic amine having 0-6 alkyl carbon atoms, stabilized against discoloration during storage by having added thereto .O5%0.5% of boric acid.

4. A product comprising xylidine and a sufficient amount of boric acid to stabilize said Xylidine against discoloration during storage.

5. The method of stabilizing xylidine against discoloration during storage which comprises adding thereto about .05%-0.5% of boric acid.

ROBERT K. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,040,665 Gruter Oct. 8, 1912 1,947,578 Bond Feb. 20, 1934 FOREIGN PATENTS Number Country Date 545,500 Great Britain May 29, 1942 

